[sdiy] Simple DSP as VCO substitute (was Re: CEM3340 reissue)

[Vladimir Pantelic]

STM32F303 has 3 12-bit DACs and a ton of 12 bit ADC channels. so saw,
square, triangle and sine via an external shaper for extra grit :)

On Jun 14, 2016 7:54 PM, "Tim Ressel" <timr at circuitabbey.com> wrote:
>
> Two DAC output yields 2 waveforms. I'm thinking sine and triangle. A
digital out pin can make squares and PWMs, or a comparator can handle it.
If you make triangles rather than sawtooths then the DAC holds together
better at higher frequencies. It is a simple matter of converting a tri to
a saw externally.
>
> I don't see 12 bit ADCs as much of a limitation. It should do V/Oct out
to 10 octaves.
>
> --TimR
>
>
> On 6/14/2016 10:40 AM, Tom Wiltshire wrote:
>>
>> On 14 Jun 2016, at 16:44, Tim Ressel <timr at circuitabbey.com> wrote:
>>
>>> Speaking of doable, it should be possible to take a DSP chip and mimic
the function of a 3340. Yes I know, the 3340 has "that sound". But it also
has "that price". I'm thinking the DSPIC33FJ128GP802. It comes in a 28 pin
dip and has built-in audio DACs. Might be interesting.
>>
>>
>> The idea had occurred to me too, for the same reasons - the dsPIC
33FJ128GP802 is about the right size and format to make a good analog
oscillator substitute. It has two DAC channels, so maybe even a dual
oscillator would be possible.
>>
>> There are definitely limitations with the chip (only six 12-bit ADC
inputs when using the DAC, for example), and moving to a digital chip
implies doing certain things differently (you won't get multiple waveform
outputs in parallel, for instance). It's a good idea, and one I've played
with quite often, but never been happy enough with the result. That won't
stop me trying again though.
>>
>> In some ways, I think it might make more sense to go in the direction of
my 8-bit PIC VCDO and give up with pure virtual analog and accept that you
can do a better job if you don't try and be something you're not. Perhaps
it should be a voltage-controlled digital oscillator chip, doing a few of
the interesting things you can do digitally instead of trying to do
anti-aliased analog waveforms with hard sync and PWM and so forth.
>>
>> Tom
>>
>>
>>
>
> --
> --Tim Ressel
> Circuit Abbey
> timr at circuitabbey.com
>
>
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